Fix various RP2040 audio dma things: (see detailed commit message)

1. Check for correct error values from dma_claim_unused_channel.
2. Introduce a .stereo flag for simplicity.
3. Clarify PWM carrier frequency choice.
4. Start introducing quiescent audio value. Still need to ramp up/down.
5. Redo audio stop logic a bit.
6. Fix (unrelated) displayio dependency things.

There is still an interference problem between other DMA users and audio. Still debugging this.

ports/raspberrypi/audio_dma.c

@@ -169,15 +169,20 @@ audio_dma_result audio_dma_setup_playback(audio_dma_t *dma,
     uint8_t dma_trigger_source) {
     // Use two DMA channels to play because the DMA can't wrap to itself without the
     // buffer being power of two aligned.
-    dma->channel[0] = dma_claim_unused_channel(false);
-    dma->channel[1] = dma_claim_unused_channel(false);
-    if (dma->channel[0] == NUM_DMA_CHANNELS || dma->channel[1] == NUM_DMA_CHANNELS) {
-        if (dma->channel[0] < NUM_DMA_CHANNELS) {
-            dma_channel_unclaim(dma->channel[0]);
-        }
+    int dma_channel_0_maybe = dma_claim_unused_channel(false);
+    if (dma_channel_0_maybe < 0) {
         return AUDIO_DMA_DMA_BUSY;
     }
 
+    int dma_channel_1_maybe = dma_claim_unused_channel(false);
+    if (dma_channel_1_maybe < 0) {
+        dma_channel_unclaim((uint)dma_channel_0_maybe);
+        return AUDIO_DMA_DMA_BUSY;
+    }
+
+    dma->channel[0] = (uint8_t)dma_channel_0_maybe;
+    dma->channel[1] = (uint8_t)dma_channel_1_maybe;
+
     dma->sample = sample;
     dma->loop = loop;
     dma->single_channel_output = single_channel_output;

ports/raspberrypi/common-hal/audiobusio/I2SOut.c

@@ -145,7 +145,13 @@ void common_hal_audiobusio_i2sout_deinit(audiobusio_i2sout_obj_t *self) {
         return;
     }
 
+    if (common_hal_audiobusio_i2sout_get_playing(self)) {
+        common_hal_audiobusio_i2sout_stop(self);
+    }
+
     common_hal_rp2pio_statemachine_deinit(&self->state_machine);
+
+    audio_dma_deinit(&self->dma);
 }
 
 void common_hal_audiobusio_i2sout_play(audiobusio_i2sout_obj_t *self,
@@ -153,6 +159,7 @@ void common_hal_audiobusio_i2sout_play(audiobusio_i2sout_obj_t *self,
     if (common_hal_audiobusio_i2sout_get_playing(self)) {
         common_hal_audiobusio_i2sout_stop(self);
     }
+
     uint8_t bits_per_sample = audiosample_bits_per_sample(sample);
     // Make sure we transmit a minimum of 16 bits.
     // TODO: Maybe we need an intermediate object to upsample instead. This is

ports/raspberrypi/common-hal/audiopwmio/PWMAudioOut.c

@@ -46,6 +46,12 @@
 
 #define NUM_DMA_TIMERS 4
 
+// The PWM clock frequency is base_clock_rate / PWM_TOP, typically 125_000_000 / PWM_TOP.
+// We pick BITS_PER_SAMPLE so we get a clock frequency that is above what would cause aliasing.
+#define BITS_PER_SAMPLE 10
+#define SAMPLE_BITS_TO_DISCARD (16 - BITS_PER_SAMPLE)
+#define PWM_TOP ((1 << BITS_PER_SAMPLE) - 1)
+
 void audiopwmout_reset() {
     for (size_t i = 0; i < NUM_DMA_TIMERS; i++) {
         dma_hw->timer[i] = 0;
@@ -55,7 +61,10 @@ void audiopwmout_reset() {
 // Caller validates that pins are free.
 void common_hal_audiopwmio_pwmaudioout_construct(audiopwmio_pwmaudioout_obj_t *self,
     const mcu_pin_obj_t *left_channel, const mcu_pin_obj_t *right_channel, uint16_t quiescent_value) {
-    if (left_channel != NULL && right_channel != NULL) {
+
+    self->stereo = right_channel != NULL;
+
+    if (self->stereo) {
         if (pwm_gpio_to_slice_num(left_channel->number) != pwm_gpio_to_slice_num(right_channel->number)) {
             mp_raise_ValueError(translate("Pins must share PWM slice"));
         }
@@ -72,22 +81,20 @@ void common_hal_audiopwmio_pwmaudioout_construct(audiopwmio_pwmaudioout_obj_t *s
     // we want. ;-) We mark ourselves variable only if we're a mono output to
     // prevent other PWM use on the other channel. If stereo, we say fixed
     // frequency so we can allocate with ourselves.
-    bool mono = right_channel == NULL;
 
-    // We don't actually know our frequency yet so just pick one that shouldn't
-    // match anyone else. (We'll only know the frequency once we play something
-    // back.)
-    uint32_t frequency = 12500;
+    // We don't actually know our frequency yet. It is set when
+    // pwmio_pwmout_set_top() is called. This value is unimportant; it just needs to be valid.
+    const uint32_t frequency = 12000000;
 
     // Make sure the PWMOut's are "deinited" by default.
     self->left_pwm.pin = NULL;
     self->right_pwm.pin = NULL;
 
-    pwmout_result_t result = common_hal_pwmio_pwmout_construct(&self->left_pwm,
-        left_channel, 0, frequency, mono);
+    pwmout_result_t result =
+        common_hal_pwmio_pwmout_construct(&self->left_pwm, left_channel, 0, frequency, !self->stereo);
     if (result == PWMOUT_OK && right_channel != NULL) {
-        result = common_hal_pwmio_pwmout_construct(&self->right_pwm,
-            right_channel, 0, frequency, false);
+        result =
+            common_hal_pwmio_pwmout_construct(&self->right_pwm, right_channel, 0, frequency, false);
         if (result != PWMOUT_OK) {
             common_hal_pwmio_pwmout_deinit(&self->left_pwm);
         }
@@ -96,10 +103,16 @@ void common_hal_audiopwmio_pwmaudioout_construct(audiopwmio_pwmaudioout_obj_t *s
         mp_raise_RuntimeError(translate("All timers in use"));
     }
 
+    self->quiescent_value = quiescent_value >> SAMPLE_BITS_TO_DISCARD;
+    common_hal_pwmio_pwmout_set_duty_cycle(&self->left_pwm, self->quiescent_value);
+    pwmio_pwmout_set_top(&self->left_pwm, PWM_TOP);
+    if (self->stereo) {
+        common_hal_pwmio_pwmout_set_duty_cycle(&self->right_pwm, self->quiescent_value);
+        pwmio_pwmout_set_top(&self->right_pwm, PWM_TOP);
+    }
+
     audio_dma_init(&self->dma);
     self->pacing_timer = NUM_DMA_TIMERS;
-
-    self->quiescent_value = quiescent_value;
 }
 
 bool common_hal_audiopwmio_pwmaudioout_deinited(audiopwmio_pwmaudioout_obj_t *self) {
@@ -110,6 +123,7 @@ void common_hal_audiopwmio_pwmaudioout_deinit(audiopwmio_pwmaudioout_obj_t *self
     if (common_hal_audiopwmio_pwmaudioout_deinited(self)) {
         return;
     }
+
     if (common_hal_audiopwmio_pwmaudioout_get_playing(self)) {
         common_hal_audiopwmio_pwmaudioout_stop(self);
     }
@@ -139,13 +153,11 @@ void common_hal_audiopwmio_pwmaudioout_play(audiopwmio_pwmaudioout_obj_t *self,
         mp_raise_RuntimeError(translate("No DMA pacing timer found"));
     }
     uint32_t tx_register = (uint32_t)&pwm_hw->slice[self->left_pwm.slice].cc;
-    if (common_hal_pwmio_pwmout_deinited(&self->right_pwm)) {
-        // Shift the destination if we are outputting to the second PWM channel.
+    if (self->stereo) {
+        // Shift the destination if we are outputting to both PWM channels.
         tx_register += self->left_pwm.channel * sizeof(uint16_t);
     }
 
-    pwmio_pwmout_set_top(&self->left_pwm, 1023);
-
     audio_dma_result result = audio_dma_setup_playback(
         &self->dma,
         sample,
@@ -153,15 +165,16 @@ void common_hal_audiopwmio_pwmaudioout_play(audiopwmio_pwmaudioout_obj_t *self,
         false, // single channel
         0, // audio channel
         false,  // output signed
-        10,
-        (uint32_t)tx_register,  // output register
+        BITS_PER_SAMPLE,
+        (uint32_t)tx_register,  // output register: PWM cc register
         0x3b + pacing_timer); // data request line
 
     if (result == AUDIO_DMA_DMA_BUSY) {
-        // common_hal_audiobusio_i2sout_stop(self);
+        common_hal_audiopwmio_pwmaudioout_stop(self);
         mp_raise_RuntimeError(translate("No DMA channel found"));
-    } else if (result == AUDIO_DMA_MEMORY_ERROR) {
-        // common_hal_audiobusio_i2sout_stop(self);
+    }
+    if (result == AUDIO_DMA_MEMORY_ERROR) {
+        common_hal_audiopwmio_pwmaudioout_stop(self);
         mp_raise_RuntimeError(translate("Unable to allocate buffers for signed conversion"));
     }
 
@@ -177,6 +190,7 @@ void common_hal_audiopwmio_pwmaudioout_play(audiopwmio_pwmaudioout_obj_t *self,
     // are 16-bit.
 
     uint32_t sample_rate = audiosample_sample_rate(sample);
+
     uint32_t system_clock = common_hal_mcu_processor_get_frequency();
     uint32_t best_numerator = 0;
     uint32_t best_denominator = 0;
@@ -204,19 +218,25 @@ void common_hal_audiopwmio_pwmaudioout_play(audiopwmio_pwmaudioout_obj_t *self,
 }
 
 void common_hal_audiopwmio_pwmaudioout_stop(audiopwmio_pwmaudioout_obj_t *self) {
-    dma_hw->timer[self->pacing_timer] = 0;
-    self->pacing_timer = NUM_DMA_TIMERS;
+    if (self->pacing_timer < NUM_DMA_TIMERS) {
+        dma_hw->timer[self->pacing_timer] = 0;
+        self->pacing_timer = NUM_DMA_TIMERS;
+    }
 
     audio_dma_stop(&self->dma);
+
+    // Set to quiescent level.
+    pwm_hw->slice[self->left_pwm.slice].cc = self->quiescent_value;
+    if (self->stereo) {
+        pwm_hw->slice[self->right_pwm.slice].cc = self->quiescent_value;
+    }
 }
 
 bool common_hal_audiopwmio_pwmaudioout_get_playing(audiopwmio_pwmaudioout_obj_t *self) {
     bool playing = audio_dma_get_playing(&self->dma);
-    if (!playing && self->pacing_timer < NUM_DMA_TIMERS) {
-        dma_hw->timer[self->pacing_timer] = 0;
-        self->pacing_timer = NUM_DMA_TIMERS;
 
-        audio_dma_stop(&self->dma);
+    if (!playing && self->pacing_timer < NUM_DMA_TIMERS) {
+        common_hal_audiopwmio_pwmaudioout_stop(self);
     }
 
     return playing;

ports/raspberrypi/common-hal/audiopwmio/PWMAudioOut.h

@@ -38,6 +38,7 @@ typedef struct {
     audio_dma_t dma;
     uint16_t quiescent_value;
     uint8_t pacing_timer;
+    bool stereo;     // if false, only using left_pwm.
 } audiopwmio_pwmaudioout_obj_t;
 
 void audiopwmout_reset(void);

ports/raspberrypi/mpconfigport.mk

@@ -21,13 +21,13 @@ CIRCUITPY_ALARM ?= 1
 
 CIRCUITPY_RP2PIO ?= 1
 CIRCUITPY_NEOPIXEL_WRITE ?= $(CIRCUITPY_RP2PIO)
-CIRCUITPY_FRAMEBUFFERIO ?= 1
+CIRCUITPY_FRAMEBUFFERIO ?= $(CIRCUITPY_DISPLAYIO)
 CIRCUITPY_FULL_BUILD ?= 1
 CIRCUITPY_AUDIOMP3 ?= 1
 CIRCUITPY_BITOPS ?= 1
 CIRCUITPY_IMAGECAPTURE ?= 1
 CIRCUITPY_PWMIO ?= 1
-CIRCUITPY_RGBMATRIX ?= 1
+CIRCUITPY_RGBMATRIX ?= $(CIRCUITPY_DISPLAYIO)
 CIRCUITPY_ROTARYIO ?= 1
 CIRCUITPY_ROTARYIO_SOFTENCODER = 1